The field of the invention is furniture and the invention relates more particularly to convertible sofas which are capable of use both as a sofa and a full length bed. Typically, convertible sofas use a foldable mattress which is maintained on the surface of the sections of the bed. As the bed is unfolded, the mattress, too, is unfolded. In order for the mechanism to operate properly, the mattress must be relatively thin and, therefore, deficient in comfort.
One improved convertible sofa mechanism is disclosed in applicant's U.S. Pat. No. 773,982, filed Sept. 9, 1985. This construction utilized a pair of J-shaped channels and used full depth cushions as a mattress. The mechanism also automatically was lifted from the sofa frame by a pair of bellows. Such construction, however, was relatively expensive and a less expensive mechanism utilizing full depth mattress parts would be advantageous.